#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
int main()
{
    double *p,l;
    int n,i;
    while(~scanf("%d",&n))
	{
        l = 0;
        p = (double *)calloc(n*2,sizeof(double));
            for ( i = 0; i < n*2; i++)
            scanf("%lf", &p[i]);
            for (i = 0; i < n * 2-2; i = i + 2)
            {
                l = l + sqrt(pow(p[i] - p[i + 2], 2) + pow(p[i + 1] - p[i + 3], 2));
            }
            l=l+sqrt(pow(p[n*2-2] - p[0], 2) + pow(p[n*2-1] - p[1], 2));
            printf("hl=%.6lf\n", l);
            free(p);
    }
	return 0;
}
